This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Systemic injection of adult neural stem cells (aNSCs) into mice with experimental autoimmune encephalomyelitis (EAE) can provide a source of new oligodendrocytes that can remyelinate demyelinated or dysmyelinated axons. However, systemically-injected aNSCs often fail to differentiate and remain undifferentiated in peri-vascular domains of demyelinated lesions where they promote apoptosis of blood-born CNS-infiltrating encephalitogenic T cells. We discovered that a high molecular weight form of hyaluronan (HA), accumulates in demyelinated lesions and inhibits oligodendrocyte progenitor cell maturation. The major receptor for HA is the CD44 transmembrane glycoprotein. Our preliminary data suggest that HA and CD44 regulate functions relevant to how aNSCs behave in demyelinated lesions, including NSC differentiation and production of pro-inflammatory cytokines. We propose that CD44 and HA are critical mediators of aNSC recruitment to demyelinated lesions and that HA, at least, can regulate whether NSCs differentiate into myelinating cells or fail to differentiate and promote T cell apoptosis at perivascular domains where HA accumulates. In this study, we aim to test the hypotheses: (1) That high molecular weight HA inhibits aNSC differentiation;(2) That NSC homing to EAE lesions depends on interactions between CD44 and HA;and (3) That HA regulates the immunomodulatory activities of NSC.